First step is to identify the top and bottom pieces of the plastic case. Please refer to the image below.
Place the PCB
Place WiThumb PCB on top of the bottom piece of the plastic case as below:
Cover with the top piece
Align the top and bottom piece and apply slight pressure. You should hear a click sound when the pieces are properly assembled. Do not apply excessive pressure or the plastic case may crack. Re-align the pieces if necessary.